The present invention relates to a cross-linked vinyl chloride polymer having a remarkably improved heat stability, and more particularly to a cross-linked vinyl chloride polymer having an improved heat stability which is obtained by copolymerizing vinyl chloride or a monomer mixture containing mainly vinyl chloride with a bisphenol-modified diacrylate or dimethacrylate.
In recent years, vinyl chloride polymer moldings having no plastic luster, namely the so-called delustered moldings, are favored in various fields of use, and various delustering techniques have been developed. Especially, attention is riveted to the delustering technique using cross-linked vinyl chloride polymers as a delustering agent, since it has the advantages that an extreme decrease of mechanical characteristics as seen in a delustering technique using large quantities of fillers does not occur, that it is not accompanied by an increase in cost as seen in a delustering technique by means of coating of acrylic resins, and that a specific equipment as required in a delustering technique by means of embossing is not necessary.
Accordingly, it has been attempted to develop compositions containing various cross-linked vinyl chloride polymers. For instance, it is proposed to utilize a cross-linked vinyl chloride polymer prepared by using a cross-linking agent such as diallyl phthalate, diallyl maleate, polyethylene glycol diacrylate or polyethylene glycol dimethacrylate, as disclosed in Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 80354/1979 and No. 5843/1981. However, the cross-linked vinyl chloride polymers have a high softening point. Therefore, the processing temperature must be made high upon molding, and the cross-linked polymers obtained by using conventional cross-linking agent rather has the disadvantage that thermal deterioration cannot be avoided.